Thought we should actually have some of the Mueller Report on the thread. Here's part of the executive summary to volume 1. www.justice.gov/storage/report.pdf
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Russian Contacts with the Campaign
The social media campaign and the GRU hacking operations coincided with a series of contacts between Trump Campaign officials and individuals with ties to the Russian government. The Office investigated whether these contacts reflected or resulted in the Campaign conspiring or coordinating with Russia in its election-interference activities. Although the investigation established that the Russian government perceived it would benefit from a Trump presidency and worked to secure that outcome, and that the Campaign expected it would benefit electorally from information stolen and released through Russian efforts, the investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities.
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The Special Counsel’s Charging Decisions
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Third, the investigation established that several individuals affiliated with the Trump Campaign lied to the Office, and to Congress, about their interactions with Russian-affiliated individuals and related matters, Those lies materially impaired the investigation of Russian election interference.
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Even when individuals testified or agreed to be interviews, they sometimes provided information which was false or incomplete, leading to some of the false-statement charges described above. And the Office faced practical limits on its ability to access relevant evidence as well—numerous witnesses and subjects lived abroad, and documents were held outside the United States.
Further, the Office learned that some of the individuals we interviewed or whose conduct we investigated—including some associated with the Trump Campaign—deleted relevant communications or communicated during the relevant period using applications that feature encryption or that do not provide for long-term retention of data or communications records. [...]
Accordingly, while this report embodies factual and legal determinations that the Office believes to be accurate and complete to the greatest extent possible, given these identified gaps, the Office cannot rule out the possibility that the unavailable information would shed additional light on (or cast in a new light) the events described in the report.